This application is related to Japanese Patent Application No. 2000-392057, filed Dec. 25, 2000, the disclosure of which is hereby incorporated herein by reference.
1. Field of the Invention
The present invention relates to a magnetron sputtering system using a planar target. The magnetron sputtering system according to the present invention is effectively used for the production of a photomask blank in a sputtering process. The photomask blank is used to produce semiconductor integrated circuits.
2. Description of the Related Art
The photomask is used in a variety of fields including the production of semiconductor integrated circuits such as ICs, LSIs and the like. The photomask is basically a light shield film mainly composed of chromium or molybdenum silicon formed on a translucent substrate with a specific pattern. In recent years, market requirements for a higher level of integration among semiconductor integrated circuits have brought about a rapid advance in the miniaturization of patterns. The miniaturization of patterns in the photomask has come to require the quality of photomask blanks to be improved. It is required to reduce defects in the photomasks, resulting from the occurrence of fine particles on the photomasks.
Under these circumstances, a planar target has been used for sputtering in the production of photomask blanks used to manufacture semiconductor photomasks. FIG. 4 shows a conventional magnetron sputtering system, and FIGS. 5 and 6 show the magnetic circuit of the conventional magnetron sputtering system. In the conventional magnetron sputtering system, a rotary magnet 11 is driven on the back surface of a target electrode 5 where a thinner target 3 is installed, and a magnetic field component parallel to the front surface of a target 3 is generated over the surface of the target 3, whereby the magnetic field is formed in the direction perpendicular to the magnetic field. This allows plasma to be trapped in the magnetic field close to the target surface, with the result that the plasma density is increased.
Chromium (Cr) or molybdenum silicide (MoSi) is normally used as a target, and sputtering gas comprising such gases as oxygen gas and nitrogen gas in addition to inactive gas is employed, so as to form a thin film on such a translucent substrate as quartz and CaF2 according to the sputtering method.
The surface of the target which is eroded and positioned opposite to the substrate electrode will hereafter be called a front surface in the present disclosure.
As described above, a thin planar target has been used in the magnetron sputtering system. The cost for targets is relatively high in the production of photomask blanks. The use of thin planar targets having shorter service life makes the production cost even higher. Further, wasting a longer time in replacing the targets makes productivity poor.
To solve these problems, it has been expected to use a thicker planar target having a thickness of 15 mm or more to ensure longer service life, thereby cutting down the production cost.
In the magnetic circuit of the conventional magnetron sputtering system, however, the magnetic field does not reach a thick target surface. This makes it difficult to generate a magnetic field component parallel to the surface with a specific intensity over the entire surface of the target. If the parallel component of the magnetic field does not have a certain intensity in some portions on the surface of the target, magnetron plasma will not be produced, and sputtering does not occur in such portions. Further, if the parallel component of the magnetic field does not reach certain intensity on the target surface, some portions of the target are not eroded.
The presence of uneroded portions in the step of sputtering allows oxides or nitrides of elements constituting the target, which are fine particles deposit again on the uneroded portions. Such depositing particles will be separated from the target surface due to differences in thermal expansion where temperatures change during and after operations, and will be deposited on the thin film.
A magnetron sputtering system which makes it possible to form a high quality thin film using a thick target is desired.
The present invention has been made to solve at least some of these problems. The object of the present invention is to provide a magnetron sputtering system which generates magnetron plasma using a thick planar target having a thickness of 15 mm or more, and produce a high quality thin film.
The present inventors have designed a magnetron sputtering system which allows the magnetic field to reach the entire front surface of a thick target, and which ensures the parallel component of the magnetic field to have a specific intensity over the entire surface of the thick planar target. In other words, an improved three-dementional magnetic circuit provides a sufficient strength for the parallel component of the magnetic field so as to ensure-that magnetron plasma occurs on the target surface using a thick planar target with a thickness of 15 mm or more.
To achieve these objectives, the present invention provides a magnetron sputtering system comprising a chamber for sputtering, a target electrode installed inside the chamber, a substrate electrode installed in the chamber opposite to the target electrode, a substantially ring-shaped magnet installed enclose the side surface of the target electrode, and a substantially semi-circular disk shaped magnet installed opposite to the target-mounted surface of the target electrode, wherein the semi-circular disk shaped magnet is rotated in the circumferential direction of the target electrode and is magnetized in the direction perpendicular to the surface of the target electrode. The semi-circular disk shaped magnet and the ring-shaped magnet are preferred to be arranged in such a way that (1) an axis connecting magnetic poles of the semi-circular disk shaped magnet is perpendicular to the surface of the semi-circular disk shaped magnet, (2) the inner surface of the ring-shaped magnet is a south pole and the outer surface is a north pole when the target electrode side of the semi-circular disk shaped magnet is a north pole and the surface not in contact with the target electrode is a south pole; and (3) the inner surface of the ring-shaped magnet is a north pole and the outer surface is a south pole when the target electrode side of the semi-circular disk shaped magnet is a south pole and the surface not in contact with the target electrode is a north pole.
It is preferred that the target installed on the aforementioned target electrode is a planar target, and the aforementioned target have a thickness of 15 mm or more. It is also preferred that the aforementioned chamber comprises a reaction gas supply means.
Further, the present invention provides a photomask blank production method characterized in that films are formed by a magnetron sputtering system according to any of the above-mentioned constructions.
In the sputtering process, an erosion of the target occurs over the entire surface of the thick planar target, without generating any fine particles including oxides and nitrides re-deposited on the target. The present invention provides a high quality photomask blank without any particles generated by separation of the aforementioned fine particles.
The system of the present invention allows the parallel component of the magnetic field obtained over all-surfaces of the thick planar target, whereby the entire surface of the thick planar target can be eroded. The thick target is characterized by a lower production cost and a longer service life in producing a photomask blank. The use of the system according to the present invention generates the parallel component having a specific magnetic field on the surface of the thick target. This solves the problem that is caused by ununiform erosion of the target during the sputtering using a thick target. Further, there is no portion where the target is not eroded. This prevents from generating particles of oxides or nitrates of elements constituting the target, and allows a higher quality photomask blank to be manufactured. As described above, a higher quality photomask blank can be manufactured at a lower cost by the sputtering system according to the present invention.